Welded thin steel boiler



July 30, 1935. w. o. LUM ET AL 2,009,852

WELDED THIN STEEL BOILER Filed Jan. 27, 1934 7g Inventors:

45 glalljcev O. Lwrn,

Ellio b r'rihgco'n,

by f. (MI/KM! v Thei Attorney Patented July 30, 1935 UNITED STATESPATENT OFFICE WELDED THIN STEEL BOILER Application January 27, 1934,Serial No. 708,648

10 Claims.

This invention relates to boiler furnaces, particularly of the weldedsteel, domestic heating type, and has for its principal object animproved construction for obtaining increased lightness and ease ofhandling without sacrificing strength and safety, and for securing atthe same time increased heating capacity and efiiciency with a minimumvolumetric displacement.

More specifically, an object of this invention has been the provision ofan improved boiler furnace, having sumcient capacity for installation inan ordinary domestic hot water or steam heating system, which may betransported as a unit through doors and like openings and may beinstalled without special foundation in a small space.

Another object has been the provision of an improved design for aninternally fired boiler of welded steel construction having awater-backed combustion chamber and secondary heat absorption passage,whereby a maximum of heat transfer area is provided with a minimum ofoverall size.

A further object of this invention has been the provision of a simpleand inexpensive unitary boiler having suflicient capacity forinstallation in a domestic heating system, which is so designed that itwill be strong and safe and yet may be constructed of such thin sheetmetal that it will be very light in weight and portable.

It is customary to construct boiler walls of relatively thick metal, notonly to provide suflicient strength but to insure a safety factor ofthickness so that corrosion over a period of time will not weaken thestructure to a dangerous degree. It is preferable to construct theboiler walls of corrosion resistant material but it is impractical to doso, due to excessive -cost of non-corrosive metal, unless the metal isin the form of very thin sheets. Hence it has been a still furtherobject of this invention to produce a design for a boiler wherein verythin non-corrosive sheet metal may be used practically, and whereinsufiicient strength is insured by preforming the various pressureresisting walls of the boiler to the contours which they will tendnaturally to assume when the boiler is under pressure.

An additional object of this invention has been the provision of animproved combustion chamber lining.

It is well known that a, hollow sphere is the best form of vessel forresistance to internal pressure. In such a vessel the stresses set up inthe walls by the pressure are equal in all directions and the strengthof the unit is determined solely by the tensile strength of the materialof which the walls are constructed. Furthermore, the internal pressurewill tend to 'cause the vessel to retain its true spherical form, sothat the walls will be self-supporting without the use 5 of auxiliarybracing. However, it is impractical to design a. boiler in the form of atrue sphere due to construction difficulties encountered and to the factthat the heat transfer area obtained for a given volume is small. Aclose approximation to the advantageous characteristics encountered inthe spherical form of vessel may be obtained by a boiler constructionwherein the various pressure resisting walls are of a shape closelyapproximating that which they would naturally tend to assume underinternal pressure which would result in all parts thereof beingsubjected solely to pure tensile stresses. We have kept in mind theabove-outlined considerations in designing an eflicient and practicalboiler wherein curved or arched 'contours are used in the constructionof the walls of all of the water and vapor chambers of our improvedboiler furnace. The advantages of such construction will be more fullyset forth hereinafter.

Our invention will be described and shown herein in its preferredembodiment as incorporated in a vertical type boiler furnace whereincombustion may be produced in a manner such as that set forth in thecopending application of Aldo Macchi, Serial No. 505,867, filed December31, 1930, which application is assigned to the assignee of the presentinvention. However, it is to be understood that we have so described andshown our invention for purposes of illustration only, and it will beapparent that various features thereof may be employed in otherembodiments where their peculiarcharacteristics make it advantageous todo so.

In the accompanying drawing Fig. 1 is a sectional elevation of theessential elements of our improved boiler furnace in its preferredembodiment, and Fig. 2 is a plan view partially in section showing moreclearly the configuration of the pressure resisting walls and thearrangement of the combustion chamber lining.

Referring to the drawing, the combustion chamber III of the boilerfurnace is of elongated substantially cylindrical shape as defined bythe hollow thin sheet metal shell I l which forms the walls therefor.Longitudinally extending corrugations l2, of a configuration later to bediscussed, are formed around the entire periphery of the shell H withthe ends of the corrugations flattened as shown at l3 and I3 to form anannular flange at each end of the shell.

Since one of the principal objectives of our invention has been thedesign of a boiler which is of relatively small size, we have found itdesirable to secure a maximum heat transfer surface for a minimum ofcombustion chamber size. This objective we have attained by the use of acorrugated combustion chamber wall whereby the heating surface of thechamber is materially increased for a given size over that which wouldbe possible were the walls of a plain cylindrical form. We have furtherconserved space by constructing the heat resisting lining for thecombustion chamber in the form of sectional refractories I4 of suchshape that they may be seated in the internally facing concave portionsof the corrugations l2 with their inner surfaces substantially flushwith the internalperiphery of the combustion chamber wall, therebyreducing the overall dimension for a given combustion chamber diameter.These refractories are supported on hangers l5 suspended from ring I6which rests upon the shoulder formed by the annular flange I3 at theupper end of the shell Ii. The combustion chamber lining provided by therefractories seated in each of the corrugations is continuous except forthe small vertically extending spaces as shown which are provided totake care of expansion. It is to be noted that due to the taperedcross-sectional form of the refractories, a maximum depth of heatresisting material is interposed between the combustion zone and thebottom surfaces of the corrugations where there is the least waterbacking, thus affording, as is desirable, a maximum protection at thesepoints.

Tightly telescoped about the shell H is a noncorrugated cylindrical thinsheet metal shell l1, having external flanges l8 and I8 respectively atthe upper and lower ends thereof, which cooperates with the shell II toform a water storage tank backing the combustion chamber. This waterstorage tank is divided into a plurality of water legs 21 as defined bythe externally facing concave portions of the corrugations l2 in theinner shell II. The shell I! is securely joined to the shell ll alongthe external surfaces or apexes of each of the respective corrugationsby welding or other suitable means as shown at 20. The upper end of thewater storage tank formed by the shells H and i1, hereinafter called theinner tank, is closed by means of a flanged ring 22 joined by welding orother suitable means to the flanged ends l3 and I8 of the shells l I andI1 respectively, thus forming a header 23 which provides communicationat their upper ends between the individual water legs 2| of the innertank. Joined to the lower flanged end l3 of the shell II is a flangedring 24 which is joined to and cooperates with a circular plate 25 toclose the lower end of the combustion chamber. Said plate 25 extendsoutwardly past the ring 24 and is joined to the flanged end IQ of theshell l'l. By the cooperation of the lower ends of the shells II and IS,the ring 24 and the plate 25, there is formed a closure for the lowerends of the inner tankand also a header 26 providing communicationbetween the lower end of the individual water legs 2| of the inner tank.

The inner tank above described is supported upon a water storage header2! and in axial alinement therewith. The header 21 in turn is mountedupon the circular base ring 30 by means of the flanged joint 3|. Thewater storage heeder 21 is formed of thin sheet metal in the shape of atorus or annular hollow tube having a circular cross-section for reasonshereinafter set forth. The inner circumference of the torus is providedwith a flange 32 upon which is mounted, centrally of the torus andcoaxially with the combustion chamber, a conduit 33 for supplying airfrom any suitable source to the combustion chamber through an air nozzleconventionally shown at 34. Said nozzle depends from the flangedcentrally located opening 35 in the combustion chamber closure plate 25into the air chamber 36 of the conduit 33 and is adapted to discharge astream of air centrally into the combustion chamber.

The base ring 30 forms a dead air space 40 below the water storageheader 21 and a second dead air space 4| is formed between said header21 and the combustion chamber closure plate 25. Thus any heat radiateddownwardly from the combustion chamber will serve to preheat the waterin the header 21, and any further loss of heat.

through the bottom of the furnace is materially reduced by the dead airspace 40.

A second water storage tank is concentrically disposed about thepreviously described inner tank and spaced therefrom as shown at 42.This second tank comprises a pair of telescoped substantiallycylindrical thin sheet metal shells 43 and 44, the inner one of which,44, is provided with longitudinally extending corrugations 45 whichcooperate with the outer shell 43 to divide the water storage chamberformed therebetween into a plurality of individual water legs 46. Shells43 and 44 are securely joined together by welding or other suitablemeans at their points of contact, that is, along the external surfacesor apexes 41 of the corrugations 45. The upper and lower ends of thecorrugated shell 44 are flattened to form circular flanges as shown at50 and 5| respectively, while the upper and lower ends of the shell 43are provided with flanges 52 and 53 respectively. A flanged ring 54 isjoined to the upper flanged ends 50 and 52 of the shells 44 and 43respectively and cooperates therewith to form a circular header 55providing communication between the upper ends of the individual waterlegs 46, and a similar flanged ring 56 cooperates in a like manner withthe lowered flanged ends 5| and 53 respec tively of the shells 44 and 43to form a header 51 providing communication between the lower ends ofthe water legs 46.

The space 42 between the inner and outer tanks provides a secondary heatabsorption passage for the'gases from the combustion chamber. Due to thecorrugated outline of the shell 44 which forms the outer wall of thesecondary passage, the heat absorption surface will be sinuous providingthe advantage of a large transfer area for a relatively small diameteras was similarly pointed out in connection with the shell ll.

Supported vertically above the water storage tanks and coaxially withthe combustion chamber is a steam header 60 in the form of a hollow,thin stainless steel torus. In order that a combustion gas distributionchamber 6| may be formed to provide communication between the combustionchamber l0 and the secondary heat absorption passage 42, the steamheader is spaced a sufficient distance above the upper ends ofthe waterstorage tanks by means of a spacing ring 62 mounted upon the upper endof the outer tank. However, it is obvious that the steam header may bemounted directly upon the upper end of the outer tank and that the upperend of the inner tank may be made low enough to provide a space forgases to pass over the end thereof and below the steam header into thesecondary heat absorption passage 42.

A hollow tube 63 is fixedly supported in the centrally located openingof the steam header to provide for the mounting therein of a fuel burnerhead such as that conventionally shown at 64. The nozzle of the burnerhead 64 is so positioned that it may discharge fuel downwardly andcentrally into the combustion chamber where the fuel upon uniting withthe air discharged upwardly from the air nozzle 34 will producecombustion in the manner set forth in the previously referred to Macchiapplication, Serial No. 505,867.

The steam header 60 is provided with outlet pipes 65 for supplying steamtherefrom to a heating system or other device, and the water storageheader 2'! is provided with inlet pipes 56 for the return of water fromthe heating system or other device to the boiler or for supplying waterfrom outside means. Conduits Ill and II provide for circulation betweenthe steam header 60 and the upper headers 55 and 23 of the outer andinner tanks respectively, while conduits I2 and I3 similarly provide forcirculation between the water storage header 2! and the lower headers 51and 26 of the outer and inner tanks respectively. By these meanscommunication is assured for circulation of steam or water between allof the individual water legs of the water storage tanks and the steamand water headers.

At the lower end of the heat absorption passage 42 is provided acombustion gas chamber 15 enclosed within the ring 14. From thecombustion gas chamber 15 the gases may pass into the exhaust passage 16which may be provided with an explosion safety door conventionally shownat 11.

In the construction of our improved boiler furnace we havesecuredstrength and rigidity as well as lightness in weight bypreforming the walls of the various pressure containers, such as thesteam and water storage headers and the concentric water storage tanks,to the contours which they will tend to assume when subjected topressure which are, broadly speaking, those contours which approach ahollow sphere or its nearest equivalent, a hollow cylinder.

The walls of the individual water legs of the concentric water storagetanks are of a curved construction very closely approximating a halfcylinder. Thus all portions of the walls of the -water legs are placedin approximately uniform tension when the boiler is in operation and theinternal pressure will further tend to cause the walls of the water legsto assume a curved or arched contour. An additional self-strengtheningeffect is produced by the cooperation of the corrugated shell with thesurrounding plain cylindrical shell. As a result of our improved designwe are enabled to use in the construction of all pressure resistingwalls an attenuated sheet metal of a thicknes much less than is normallyrequired in the construction of boilers. We prefer to use sheet steel ofa thickness in the neighborhood of 3 5" as contrasted to a thickness inthe neighborhood of which is used in general practice. Due to the designemployed, the various elements of our boiler will retain their shapeswithout auxiliary bracing even though very thin sheet metal is used inthe construction thereof. This results in a great saving in weightwithout a sacrifice of strength and safety.

In order that the thin walls of our boiler will not become weakened bycorrosion we use stainless steel in our preferred embodiment. However,it is obvious that any other similar corrosion resisting sheet metal maybe used.

Further keeping in mind the advantages of the spherical contour in thedesign of pressure containers, we have formed the steam header 60 andthe water storage header 2'! in the shape of hollow tori or annulartubes of circular crosssection. The walls of these two headers are,therefore, subjected to uniform stress under internal pressure and areself-supporting, which enables us to use thin, stainless steel, in theconstruction thereof as in the construction of the walls of theconcentric water storage tanks. An additlonaladvantage is secured in ourpreferred embodiment in that the central openings in the torus shapedheaders afford convenient means for installation of the fuel burner headand secondary air supply means.

It will be seen that as a result of the design herein described andillustrated, we are enabled to construct a boiler furnace which has therequisite strength and safety, yet is sufficiently small and light inweight that it may be transported as a unit, moved through doors andlike openings, and installed without special foundation in locationswhere the available space is small.

It is obvious that various modifications may be made in the preferreddesign of our improved boiler furnace as herein described andillustrated without departing from our invention, and such modificationsare intended to be included within the scope of the appended claims inwhich we point out with particularity those features which we' believeto be novel.

What we claim as new and desire to secure by Letters Patent of theUnited States, is:-

1. In a boiler furnace, a container for water to be heated including incombination a hollow sheet metal shell naving longitudinal corrugations,a second sheet metal shell telescoped about said first shell andcontacting therewith along'the apexes of said corrugations to form aplurality of individual water legs, said shells being joined along thelines of contact therebetween and said corrugations being of curvedcontour so that all portions of the metal walls forming said water legswill be subjected to tension when the water therein is expanded byheating, and means providing separate headers at each end of said shellsin communication with the ends of said individual water legs.

2. In a boiler furnace, means for containing water to be heatedincluding in combination a tank comprising a substantially cylindricalsheet metal shell having longitudinl corrugations of curved contour anda second substantially cylindrical non-corrugated sheet metal shelltelescoped about said first shell and'joined thereto along the apexes ofsaid corrugations to form a plurality of individual water legs, and apair of hollow torus-shaped header members disposed one adjacent each ofthe opposite ends of said shells with connecting means between said tankand said members providing communication between the ends of saidindividual water legs and the interiors of said members, wherebysubstantially all portions of the walls of said water containing meansare under tension when the water therein is expanded by heating.

3. In a furnace, means for forming a water backed combustion chamberwall including an annular sheet metal shell surrounding the furnacecombustion zone and having corrugations of curved contour to provide asinuous heat transfer wall for the combustion chamber, a seconnon-corrugated sheet metal shell surrounding said first shell andcontacting therewith along the external apexes of said corrugations toform a plurality of individual water legs, and a plurality of refractorymembers seated in the inwardly facing depressions of said corrugationssaid refractories having tapered cross sections to fit said depressionsand substantially fill the same whereby the respective portions of thesheet metal of said first shell are heat insulated in inverse proportionto the amount of water backing behind the same.

4. In a boiler furnace, the combination of a vertically disposedsubstantially cylindrical sheet metal casing forming a combustionchamber with opposite openings in the ends thereof, said casing havinglongitudinal corrugations of curved contour, a second substantiallycylindrical sheet metal casing telescoped about said first casing andcontacting therewith along the apexes of said corrugations to form aplurality of individual water legs, a plurality of refractory membershaving a tapered cross section of such configuration that said membersfit into the inwardly facing depressions of said corrugations andsubstantially fill the same, means for removably supporting said membersin seated positions in said depressions, means for supplying water tosaid water legs, means for closing the lower one of said openings insaid combustion chamber, and a fuel burner nozzle disposed in the upperone of said openings to discharge fuel downwardly into the combustionchamber.

5. In a boiler furnace having a combustion chamber, means for forming awater and steam pressure chamber including in combination asubstantially cylindrical sheet metal shell surrounding the combustionchamber and having longitudinal corrugations of curved contour, a secondsubstantially cylindrical non-corrugated sheet metal shell telescopedabout said first shell and securely joined thereto along the exteriorapexes of said corrugations and cooperating with the exteriorly concaveportions of said corrugations to form a plurality of individual waterlegs, a hollow torus-shaped member disposed at one end of saidcombustion chamber and in axial alignment with said shells and meansproviding communication between the interior of said member and the endsof said water legs.

6. In a boiler furnace having a combustion chamber, a water chamberincluding a plurality of nested spaced apart tanks surrounding thecombustion chamber, each of said tanks comprising a pair of telescopedhollow sheet metal shells, the inner shell of each one ofsaid tankshaving corrugations of curved contour and being joined respectively tothe outer shell of each one of said tanks along the exterior apexes ofsaid corrugations to form a plurality of individual water legs, andheader means at each end of said tanks providing communication betweenthe ends of the water legs of said tanks.

7. In a boiler furnace having a combustion chamber, the combination witha plurality of concentric vertically disposed water storage tankssurrounding the combustion chamber and spaced apart to form fluepassages therebetween in communication with the combustion chamber atone end, each of said water storage tanks including contactingconcentric sheet metal shells joined at their ends and at their pointsof contact, the inner of said shells having longitudinal corrugationscooperating with the outer oi said shells to form a plurality ofcommunicating water legs, of header means comprising a pair of hollowannuli disposed respectively one above and one below said water storagetanks and coaxially therewith, means for providing communication betweensaid header means and said water legs, and fuel bumer means verticallydisposed in the center of the upper one of said annuli and adapted todischarge fuel downwardly into the combustion chamber.

8. A boiler furnace having a combustion chamber and comprisingconcentrically nested water tanks surrounding the combustion chamber andspaced apart to provide a combustion gas passage therebetweencommunicating with one end of the combustion chamber, a pair of hollowtorus shaped header members disposed one adjacent each of the oppositeends of said tanks and coaxially therewith, and conduit means betweensaid tanks and said header members to provide for circulationtherebetween.

9. A boiler furnace comprising means for forming a water backedcombustion chamber including a pair of nested contacting sheet metalshells surrounding the furnace combustion zone, the inner one of saidshells having longitudinal corrugations of curved contour securelyjoined to the outer one of said shells along the external apexes of thecorrugations and cooperating with the outer one of said shells to form aplurality of individual water legs, means for forming a water backedsecondary heat absorption chamber communicating with said combustionchamber at one end including a second pair of nested contacting sheetmetal shells, the inner one of said second pair of shells providingwithin the interior thereof a passage for combustion gases from thecombustion chamber and having longitudinal corrugations of curvedcontour securely joined to the outer one of said second pair of shellsalong the external. apexes of the corrugations and cooperating with theouter one of said second pair of shells to form a plurality ofindividual water legs, and means connected to the ends of said waterlegs for providing communication therebetween including water and steamheader members of tubular construction having circular cross sections.

10. A boiler furnace comprising a cylindrical combustion chamber havingindividual water backed heat absorbing elements disposed around thesides thereof, said elements comprising inner and outer curved metalwalls preformed to be under tension upon generation of internal pressurein the elements, a secondary heat absorbing chamber communicating withthe combustion chamber at one end thereof and extending adjacent theother end thereof and having individual water backed heat absorbingelements disposed around the sides of said secondary heat absorbingchamber, said second mentioned elements comprising inner and outercurved metal walls preformed to be under tension upon generation ofinternal pressure in the elements and conduits communicating between theelements around the combustion chamber and the elements around thesecondary chamber adjacent the ends of the combustion chamber.

WALTER. O. LUM.

ELLIOTT D. HARRINGTON.

